1. Field of the Invention
The invention relates to a device and a method for the recovery and utilization of fly ash as a source of high purity carbon, ash, and minerals, and, more specifically, this invention relates to a new device and method for isolating fly ash components on the basis of size and electrical charge.
2. Background of the Invention
Improved beneficiation and utilization schemes for fly ash can transform it from a waste material, with associated disposal costs, to a valuable product. The utilization of power-plant-derived fly ash has been impacted by recent shifts to low NOx burners which can increase the carbon content of the ash above the specification for its use in Portland cement. The ability to efficiently extract high purity carbon, ash and minerals is important in the development and application of cost-effective beneficiation technologies for fly ash separation. There is technology in use in this field, but much of the technology is carried out in aqueous solutions. Dry separation methods exist; but, they do not differentiate significantly among the different substances in a complex dry mixture such as fly ash.
Electrostatic separation methods are well known in the art. U.S. Pat. No. 3,493,109 awarded to Carta et al. on Feb. 3, 1970, discloses a method which utilizes electrostatic separation, or more specifically triboelectrostatic separation. Particles become positively charged, negatively charged, or remain electrically neutral, hence triboelectrostatic. There are other examples of the electrostatic separation process, but improvements in separation efficiency are still possible. More specifically, most prior art apparatus and methods for electrostatic separation of particles generally suffer substantial inefficiencies resulting from turbulent flow conditions.
U.S. Pat. No. 5,944,875 awarded to Stencel et al. on Aug. 31, 1999 discloses a triboelectrostatic separation apparatus having a mixing chamber, a pre-separator, and only three different means of particle egress, based on positive charge, negative charge, or neutral charge of the particle.
Another Stencel patent (U.S. Pat. No. 5,938,041 awarded on Aug. 17, 1999) discloses a triboelectrostatic separation apparatus with only three different means of particle egress.
U.S. Pat. No. 5,299,692 awarded to Nelson et al. on Apr. 5, 1994 discloses a method employing an inclined surface and two vibratory sources for concentration of fly ash into a lighter, high carbon fraction and a heavier enhanced fraction. An electrostatic charging method of separation is not provided.
U.S. Pat. No. 4,652,433 awarded to Ashworth, et al. on Mar. 24, 1987 discloses a separation method which comprises sieving, flotation, dry magnetic separation, acid leaching, and the use of ion-exchange resins. It does not provide an electrostatic method of separation.
U.S. Pat. No. 4,539,187 awarded to Russ, et al. on Sep. 3, 1985 discloses a method for the separation and recovery of substantially pure Al, Fe, and silica from fly ash. The process involves chemical steps which utilize aqueous acids and does not provide for a dry physical method of separation.
U.S. Pat. No. 4,386,057 awarded to Dobbins, et al. on May 31, 1983 discloses a method for separating and recovering iron oxide from coal fly ash via dissolution of magnetic portion of fly ash in strong alkali solution and does not provide for a dry physical method of separation.
U.S. Pat. No. 4,130,267 awarded to Russ et al. on Dec. 19, 1978 discloses a process for recovering mineral values from fly ash which includes forming an alkaline aqueous fly ash blend. Russ et al does not provide for a dry physical method of separation.
U.S. Pat. No. 4,121,945 awarded to Hurst et al. on Oct. 24, 1978 discloses a wet process for obtaining a carbon concentrate and iron concentrate from fly ash and does not provide for a dry physical method of separation.
A need exists in the art for a method and device for separating out the components of fly ash in a single phase, i.e., without the need for aqueous or nonaqueous separation techniques. The method and device should separate the components based on size and electrical charge to effect a more thorough separation result. And the method and device should allow for the separation of a myriad of different sized particles and particle charges.
An object of the present invention is to provide a method of efficiently extracting high purity carbon, ash and minerals from fly ash that overcomes many of the disadvantages of the prior art.
Another object of the present invention is to provide a new method for using triboelectrostatic separation to concentrate the different components of fly ash. A feature of the invention is that certain moieties of the ash become electrically charged while other moieties remain electrically neutral. An advantage is that all of the moieties are simultaneously separated based on their electrical charge and size.
Still another object of the present invention is to provide a method of removing unburned carbon from fly ash. A feature of the invention is imparting a positive charge to the unburned carbon. An advantage of the invention is that the positive charge on the unburned carbon facilitates its isolation from other components of the fly ash.
It is another object of the present invention to provide a device for removing selected materials from fly ash. A feature of the invention is that the device exploits size differences and electric charge differences of the materials to effect isolation of specific sized and charged materials from remainder portions of the fly ash. An advantage of the device is that a more efficient isolation of target fly ash components is realized.
Yet another object of the present invention is to provide a device for isolating particles having a certain size, from fly ash. A feature of the invention is the provision for a means to continuously remove particles, based on size, from a fly ash feed stream. An advantage of the invention is that the fractions are continuously isolated from each other based on size and/or charge, and then removed, all during operation of the device, therefore minimizing downtime during the fraction collection.
Briefly, the invention provides a process for removing organic and inorganic particles, based on their electric charge and size, from a dry mixture, comprising sizing the mixture into a plurality of particle fractions, isolating the fractions from each other; contacting the isolated fractions to a charged substrate to create charged and uncharged particles; and subjecting the particles to an electric field.
A device for separating particles from a mixture is also provided, the device comprising a means for sizing the particles; a means for contacting the particles with a means for imparting electric charge to the particles; a means for subjecting the sized particles to an electric field; and a means for separating and then collecting the particles based on particle size and charge.